Manufacture of artificial silk



Patented June 16, 1936 UNITED STATES PATENT OFFWE MANUFACTURE OFARTIFICIAL SILK Johan D. W. Hubbeling, Enka, N. 0., assignor to AmericanEnka Corporation, Enka, N. 0., a corporation of Delaware No Drawing.Application September 5, 1934. Serial No. 742,859

2 Claims. (01. 18-54) This application is a continuation in part of incommercial production. Fully delustered yarn my application, SerialNumber 651,632, filed Janucontains from 1 to 5% of titanium dioxidebased ary 13, 1933. on the cellulose content, and even though the pig-The present invention relates to the manufacment particles are initiallybroken down into an 5 ture of delustered artificial silk from cellulosicaverage particle size approximating 0.75 of a 5 solutions, to whichsolutions have been added micron, after they have been introduced intothe various kinds of pigments, and more particularly cellulosicsolution, agglomerations occur which the invention is directed tomaintaining improved when subsequently extruded through the minutespinning conditions during the process of manuopenings in thespinnerettes cause clogging of facturing threads, filaments and the likefrom the these openings, and therefore prevent practical 10 saidcellulosic solutions. spinning conditions. It has been found impossi- Itis known in the art to deluster artificial silk ble therefore, to obtaina completely homogeneous threads, filaments and the like, byincorporating distribution of the titanium pigments in a celluin thesame, various types of pigments such as losic solution when employingpure titanium barium sulphate, zinc sulphide, lithopone, and the dioxidein sufiicient amounts to fully deluster the 15 oxides of titanium,zirconium, tin, and thorium subsequently formed filaments. As soon asthe and the like. These pigments have been utilized spinnerettescommence to clog, poor quality yarn and incorporated in the artificialsilk during variresults, and the product is commercially undeous stagesin manufacturing the same. It has sirable. The operation of removing andcleaning even been attempted to add the pigments to the the spinnerettesis a tedious and expensive one, 20 artificial silk filaments after theyhave been exwhich involves not only loss of time, but, also truded intoand through coagulating baths, but shortens the life of the spinnerettesthemselves. such an operation was very impractical, in view Withinrecent years the artificial silk industry of the fact that the pigmentsdid not primarily has gradually gone through a transition period,

enter into the filaments to a suificient degree to whereby low lusteryarn has substantially taken produce the desired delustering effects.the place of the high luster yarn. It has been It has been generallyaccepted in the industry during this period that the demand for the lowafter extensive research, that the most desirable luster yarn hasgradually increased, and has results have been obtained by adding thepigment therefore forced the industry to deluster, or form to thecellulosic solution itself prior to filtering lusterless yarn byemploying the various above 30 and spinning the solution into filaments.This named pigments, or mixtures of pigments. For a addition may be madeeither in dry form or first time only very low percentages of thepigments, producing a suspension of the pigment and adding or mixturesof pigments were used, generally, mathe same to the cellulosic solution.The filtering terially below 1% based on the cellulose content.

step tends to take out the larger pigment particles This resulted in ayarn of only medium luster. 35 and effects a more thorough distributionand dis- When it was ascertained that titanium possessed persion of theparticles within the solution and the most suitable properties fordelustering purconsequently in the spun filament. poses, it was employedalone or with other pig- Of the various pigments which have beenemments, but still maintaining the total percent of ployed indelustering artificial silk, titanium pigments very low. In no casehowever, wasgany 40 dioxide is considered to be the most desirablebepigment successfully used with titanium, for the cause of the factthat it has a very high index reason that the combination did notproduce a of refraction, and therefore produces a relatively luster aslow as when titanium was employed great covering power or opacity in thefinished alone.

filament. For this reason, the invention will be At the present time twogeneral types of de- 45 described throughout, as applied specifically tolustered or lusterless yarn are manufactured. titanium dioxide, althoughin considering the in- The first type is that in which percentages ofpigventive concept in its broadest aspect, it is inments ranging below1% have been incorporated tended that this invention will include anypig- .in the cellulosic solution. The second type comme'nt which couldbe substituted for TiOz, but prises a yarn of very low luster which hasbeen 50 would ordinarily form objectionable agglomeraproduced fromcellulosic solutions containing relations within the cellulosicsolution. When pure tively high percentages of titanium dioxide. Thispigments such as titanium dioxide have been used however, presents thedifiiculties caused by clogin sufficient amounts to produce a fullydelustered ging of spinnerettes as described above.

yarn, serious difilculties have been encountered It is an object of thepresent invention to probroadly the'utilization of titanium dioxide'inpercentages greater than those hitherto employed, but in every case thespecific amounts used are dependent upon the degree of opacity desiredin the finished filament. The commercial titanium dioxide which isuniversally used, upon microscopic examination, proves to consist of twomain components: hard aggregates of titanium dioxide, and agglomerationsof loosely held individual titanium dioxide particles, the

latter do not disperse readily in water, or alkaline solutions Also,when employing this product in the viscose, a considerable percentage ofthe agglomerations is not loosened by methods hitherto known. The hardaggregates are rather readily broken down by mechanical means, such asthe use of suitable milling equipment. To obtain a uniform dispersionand to prevent a further agglomeration of the pigment particles in thecellulosic solution, barium sulphate is employed in very smallquantities, intimately admixed with the titanium dioxide, prior toincorporation into the cellulosic solution.

As in the case where pigments or mixtures of pigments have been employedin small percentages, it is of course necessary in the present processto effect a breaking down of the titanium dioxide pigment particles intoa very fine size approximating 0.75 of a micron. It has been found thatthe fine size of these particles can be maintained and evenly dispersedthroughout the celluloslc solution by intimately mixing with theparticles, barium sulphate also in very fine form.

One of the suitable methods of carrying out the process would be toemploy a special kind of compound pigment made by precipitating bariumsulphate-in a solution of the desired salt, such as titanium sulphate,and precipitating the desired delustering pigment such as titaniumdioxide on to the particles of barium sulphate. This produces anextremely intimate and finely divided mixture of barium sulphate, andtitanium dioxide. The ultimate proportions of the barium and titaniummay be varied within practical ranges. A very desirable compositionwhich has been found to give excellent results and substantially preventthe clogging of spinnerettes, is as follows:

Percent Pigments '70 Water 30,

A measured amount of this paste is introduced into a ball mill, colloidmill, or the like, which contains water for suspending the same. Thewater is preferably rendered slightly alkaline with caustic soda. vTothis suspension is added suiiicient pure titanium dioxide in powderedform phate is preferably from 0.1 to 1%.

(rayox). The amount of rayox added depends of course on the degree ofluster desired in the finished filament. The suspension is thoroughlyagitated and mixed by rotating the mill for several hours until all ofthe hard aggregates are 5 broken down to a practical particle sizeaveraging approximately 0.75 micron.

A desired portion of the suspension is added to the spinning solution,and thoroughly mixed, filtered, and allowed to age for a suitable length10 of time. It is then extruded through spinnerettes and spun intofilaments. The clogging of spinnerettes is substantially negligible, andtherefore greatly improved spinning conditions are realized. 15

As above stated, the amount of titanium dioxide employed is optional,and depends onthe degree of luster desired. Preferable ranges oftitanium dioxide are from 1 to 5% based on the cellulose content, andthe amount of barium sul- It is desirable and practical that theamountof barium sulphate is maintained as low as possible, asit does notdeluster as satisfactorily as titanium dioxide, but is only employed forthe purpose of effecting a uniform dispersion and preventing theformation of agglomerations in the spinning solution.

The improved results obtained by the addition of barium sulphate aretabulated below and compiled from a series of experiments. The tablerepresents the number of clogged spinnerettes which occurred over afixed period.

45 The above table clearly shows that the number of loose agglomerationsare materially decreased, and facilitate the commercial production ofimproved artificial silk filaments. It can further be determined fromthis table that the decrease in the percent of loose agglomerations andthe clogged spinnerettes is the greatest when the amounts of TiO:employed, drops from 100% to 75% and the B8304 increases from 0% to 25%in proportion to each other. It is apparent, therefore, that this is thepreferable working range.

Specific proportions which have been prepared in accordance with thepresent invention are given below by way "of example, and have beenfound to produce very satisfactory results. 60

Example-12.5 kg. of paste containing 30% water and 70% T10: and 321804of which 70% is pure T10: and 30%, pure BaSO; is mixed with 14.5 kg. ofsubstantially 100% T102. This mixture is suspended in 72 kg. of watermade alkaline by the addition of .3 kg. of 50% NaOH and the entire batchof about 80 liters in volume is placed in a ball mill and thoroughlyagitated for several hours. The total amount of T10: in the batch isapproximately 20.6 kg. and BaS04 is 2.6 kg. The proportion of TiO: toBaSO4 is approximately 8: 1. 15 liters of the batch is added to a tankof viscose of 1400 liters capacity containing about 7% or 113.64 kg. ofcellulose and after thorough mixing is ready to be filtered and 75solution and an amount of B8504 sufilcient to spun into filaments. Theamount of TiOz in the filaments is approximately 3.4% based on thecellulose content and the amount of BaSO is approximately 0.4%.

It is to be understood that the invention is not restricted to theprecise proportions as set forth in the preceding examples since it isobvious that the proportions of the pigments may vary within wide limitsdepending on the degree of opacity or decrease in luster desired.

What I claim is:

1. A process for the manufacture of delustered artificial silk filamentsfrom cellulosic solutions by spinning the same through spinneretteswhich comprises incorporating in the cellulosic solution an amount ofTiOz of the order of about 1% or more based on the cellulose content ofthe substantially prevent the formation of agglomerations of a. naturetending to clog the openings Y in the spinnerettes, and thereafterspinning the cellulosic solution to form filaments, the amount of BaSO4being approximately 1:8 to the amount of TiOz.

2. A process for the manufacture of delustered artificial silk filamentsfrom cellulosic solutions according to the wet spinning method whichcomprises incorporating in the cellulosic solution a mixture of TiOz inamount approximating 3.4% based on the cellulose content of the solutionand an amount of BaSO4 approximating 0.4% based on the cellulosecontent, and thereafter spinning 15 the cellulosic solution to formfilaments.

JOHAN D. W. HUBBELING.

